1. Field
The present disclosure relates to a rotor for a rotary electric machine.
2. Description of the Related Art
A conventionally known rotor used for a rotary electric machine utilizes a rotor core which is formed by stacking a plurality of magnetic steel plates (see, for example, FIG. 17, FIG. 18, and Japanese Patent No. 5118920).
A conventional rotor 100 for a rotary electric machine as illustrated in FIG. 18 is formed of a plurality of stacked steel plates 101, and includes a rotor core 105 having a plurality of magnet insertion holes 103 which are formed at every first circumferential space (45° space), permanent magnets (not illustrated) each of which is inserted in a corresponding magnet insertion hole 103, and a rotor shaft (not illustrated) inserted in a shaft hole 107 which is formed at the center of each rotor core 105.
As illustrated in FIG. 17, the steel plate 101 included in the rotor core 105 has magnet insertion piece holes 103a which are formed at every first circumferential space (45° space), and a plurality of through piece holes 109a which axially penetrate the steel plate 101 at every second circumferential space (45° space) in a circumferential direction on the radially inner side of the magnet insertion piece holes 103a. 
In the steel plate 101, a radially inner side annular ring 111a formed radially inward of the through piece holes 109a, and a radially outer side annular ring 113a formed radially outward of the through piece holes 109a are connected by a plurality of ribs 115 which are formed between the through piece holes 109a. 
The rotor core 105 is formed by stacking a plurality of steel plates 101 having the same shape in the axial direction, and includes the magnet insertion holes 103 each formed of corresponding magnet insertion piece holes 103a of the steel plates 101, through holes 109 each formed of corresponding through piece holes 109a of the steel plates 101, and a radially inner side rotor core 111 and a radially outer side rotor core 113 which are respectively formed of the radially inner side annular rings 111a and the radially outer side annular rings 113a of the steel plates 101. That is, the rotor core 105 is in a shape achieved by extending a steel plate 101 in the stacking direction (the axial direction).
Also, in order to reduce nonuniform thickness of the stacked steel plates 101, the rotor core 105 may be formed such that one steel plate 101 axially adjacent to another steel plate 101 is rotated for the first circumferential space (45°) in a circumferential direction and stacked. Even in this case, because the first and second circumferential spaces have the same 45° space, the through piece holes 109a of axially adjacent steel plates 101 overlap when viewed in the axial direction, and the rotor core 105 is in the shape achieved by extending a steel plate 101 in the stacking direction (the axial direction).
However, in such a rotor core 105, the ribs 115 of the stacked steel plates 101 overlap when viewed in the axial direction, and thus stress concentration occurs at a radially inner side connecting portion 117 between the ribs 115 and the radially inner side annular ring 111a (the radially inner side rotor core 111). Therefore, in order to maintain the strength of the rotor core 105, it is preferable to increase the thickness of the radially inner side annular ring 111a (the radially inner side rotor core 111) locally at circumferentially overlapping area with the radially inner side connecting portion 117 and to increase the thickness of a rotor shaft locally which is to be inserted in the shaft hole 107. Practically, it is preferable to increase the thickness of the entire radially inner side annular ring 111a (the radially inner side rotor core 111) and to increase the thickness of the entire rotor shaft.
Because each through hole 109 is in the shape achieved by extending a through piece hole 109a in the axial direction, in the case where oil flows into a through hole 109 from a gap between the stacked steel plates 101 in the environment of oil (for liquid cooling), oil may be densely trapped in a particular one of the through holes 109. Such densely trapped oil in a particular through hole 109 may cause eccentricity (unbalance) of the rotor 100, and vibration and/or sound increase at the time of rotation, thereby reducing the marketability.
Thus, a solution to solve these problems may be given by using the rotor for a rotary electric machine described in Japanese Patent No. 5118920. The rotor for a rotary electric machine described in Japanese Patent No. 5118920 is fixed to a rotor shaft and includes a rotor core having a cooling medium passage. The rotor core is formed by stacking first and second plate-shaped members in the axial direction.
The first plate-shaped member has a first hole part that partially constitutes the cooling medium passage, and a first rotation regulation unit that is fitted into the rotor shaft and configured to regulate the rotation of the first plate-shaped member with respect to the rotor shaft. The second plate-shaped member is formed at a position which is circumferentially displaced with respect to the first hole part, and has a second hole part that partially constitutes the cooling medium passage, and a second rotation regulation unit that is fitted into the rotor shaft and configured to regulate the rotation of the second plate-shaped member with respect to the rotor shaft.
Stacking the first and second plate-shaped members in the axial direction allows communication between the first and second hole parts which are formed at circumferentially displaced positions, and when the first and second hole parts are overlapped, the hole parts are formed so as to surround the entire circumference of the rotor shaft as a whole. With this configuration, a cooling medium is supplied uniformly in the circumferential direction of the rotor core. Also, a rib between circumferentially adjacent first hole parts and a rib between circumferentially adjacent second hole parts are formed at circumferentially displaced positions, and thus concentration of a stress on the root of a rib may be reduced.